Polar coded track circuit railway signaling system



Aug. 13, 1957 c. E. STAPLES POLAR CODED-TRACK CIRCUIT RAILWAY SIGNALING SYSTEM Filed May 11, 1951 2 Sheets-Sheet l v .INVENTOR.

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POLAR CODED TRACK CIRCUIT RAILWAY SIGNALING SYSTEM 2 Sheets-Sheet 2 VQQ INVENTOR.

Crawford E Staples BY w. of HIS A 'i 'amm w Ema 5% Q mm N Q M $5 QQ S QNN LMNM I m EHNWHM mw E HT I m, 5% \ll RN$ Aug. 13, 1957 Filed May 11, 1951 |||||||||ll||||l POLAR CODED TRACK CIRCUIT RAILWA SIGNALING SYSTEM Crawford E. Staples, Pittsburgh, Pa., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Application May 11, 1951, Serial No. 225,858

7 Claims. (Cl. 246-34) My invention relates to railway signaling systems, and particularly to an improved railway signaling system employing coded track circuits of the polar type.

In an application for Letters Patent of the United States, Serial No. 674,436, filed June 5, 1946, by Henry 8. Young, now U. S. Patent No. 2,558,473, granted on June 26, 1951, there is shown a signaling system for use on single track railroads over which traffic may move in either direction. This system is designed for use on stretches of railway where trains are relatively infrequent, and accordingly, no provision is made for following moves. That is, the system is arranged so that when'a first train is moving through the single track stretch in either direction, a second train moving in the same direction is not permitted to enter the single track stretch until the first train has vacated the stretch, 'In certain instances, it is desirable to permit a second train to enter States Patent Patented Aug. 13, 1957 are provided in the single track stretch in advance of each leaving signal, and which intermediate signals govern the polarity of code impulses transmitted toward the leaving signal, in accordance with traffic conditions in the stretch in advance of the intermediate signal to thereby provide a caution indication on the leaving signal.

Another object of my invention is to provide a system of the type described in which an intermediate signal in advance of each leaving signal governs the supply of coded energy supplied over the track stretch between the intermediate signal and the leaving signal in such manner that coded energy of a first or a second polarity is supthe stretch of single track before the preceding train of the stretch to the other in opposite directions, as long as the stretch is unoccupied. When a train occupies a single track stretch the supply of code impulses from the end at which the train enters is cut off, thereby placing all the opposing signals at stop, and the supply of code impulses from the other end of the stretch is continued to hold the signals clear in advance of the train. In the Young system, the signal governing the train movement into the single track stretch is held at stop while a train occupies the stretch. When the stretch is vacated, code impulses are again supplied through the various track sections so that the signals can clear for subsequent train movements.

It may, under certain circumstances, be desirable to permit the signals governing movements into the single track stretch to provide a caution indication aspect to thereby permit a following train to move into the single track stretch before the stretch is vacated by a preceding train.

An object, of my invention is to provide an improved system of the type described in which leaving signals which govern train movements into a single track stretch are controlled in such manner as to permit following moves to be made into the single track stretch. I

Another object of my invention is to provide a system of the type described in which the leavingsignals are governed in accordance with the traffic conditions in.

advance to provide a caution indication when the single track stretch in advance of the signal is occupied by a train moving away from said leaving signal.

A further object of my invention is to provide a system of the type described in which intermediate signals plied to govern the leaving signal so as to display a clear or caution aspect, depending upon whether a train moving away from the intermediate signal occupies the single track stretch. v

' Other objects of my invention and features of novelty thereof will become apparent from the following description taken in connection with the accompanying drawings.

I shall describe one form of railway signaling system employing polar coded track circuits which embodies my invention, and shall then point out the novel features thereof in claims.

In practicing my invention, I provide, in addition to the arrangement shown in'the aforementioned Young application, an intermediate signal opposite the distant signal for each headblock, or siding entering signal. This signal is governed by the occupancy of the section of single track stretch extending in advance of the intermediate signal to the other end of the stretch. A directional stick relay associated withthe intermediate signal is controlled in such manner as to be energized and have its contacts'picked up when a train moves by the intermediate signal in the direction in which the signal governs traffic, and to remain picked up until the train vacates the portion of the stretch governed by the intermediate signal. Contacts of this stick relay govern the supply of coded energy to the end section of the single track stretch extending rearwardly from the intermediatesignal to the headblock signal in such manner that coded energy of one polarity is supplied thereto when the stick relay is released, and coded energyof the opposite polarity is SUP'. plied thereto when the stick relay is picked up. At the leaving signal, code responsive apparatus is provided which governs the leaving signal to display either a cantion aspect or a clear aspect in accordance with the polarity of the received energy. As a result, the leaving signal will display a caution aspect to permit a following train to enter the single track stretch after a preceding train has passed the intermediate signal. i

In the drawings, Figs. 1a and 1b, arranged side by side. in the order named with Fig. 1a at the left, show the track plan and circuits associated with a single track stretch of railway equipped with apparatus embodying my invention. Fig. 1a shows the circuits at the right-hand or east end of a passing siding A and the circuits and equipment located at the distant signal for this siding, together with associated intermediate signal, while Fig. 1b shows the circuits at the left-hand or west end of another passing siding O, and at the associated distant and intermediate signal. 1

In this system, the single track stretch between passing sidings is divided by insulated joints in the track ing fromthe end of the passing siding to the distant signal for the siding at which point is located the intermediate signal referred to previously. The portion-of the single track stretch between the intermediate signals may form one or more track sections, the number depending upon the length of this portion of the stretch. If more than one track section is required, the supply of coded energy in both directions is repeated between sections by conventional front contact coding cut section equipment, well-known in the art. In the drawings, the single track portion between the distant signals in either direction is shown as including only a single track circuit, in order to simplify the disclosure.

The entering signals 88 and PS, which govern the movement of traffic from the single track stretch into the section of track beside the passing siding may be controlled in any manner well-known in the art, and such control is not shown in these drawings nor described, since it forms no part of my invention. One manner in' which these signals may be controlled is shown in the aforementioned Young application.

All of the signals shown in the drawings are of the well-known color light type, having three lamps, a green lamp which when lighted indicates clear, a yellow lamp which when lighted indicates caution, and a red lamp which when lighted indicates stop, or, as in the case of the intermediate signals, having only a green and red light which indicates clear and stop, respectively, when lighted. V At each of the signal locations energy for the operation of the apparatus other than the coded track circuit equipment is supplied by a suitable source of'direct current such as the batteries shown in the drawings, the terminals of which are designated by the reference characters B and N. Certain of the relays employed inthe system are of the slow acting type, and are distinguished in the drawings from conventional relays by a neutral line through the contacts having an arrowhead pointing in the direction in which the relay is slow acting, e. g., downwardly in the case of a slow release relay.

The apparatus is shown in the condition which it assumes when the single track stretch is vacant, and the operation of the apparatus under these circumstances will now be described.

As shown in Fig. 1a, the supply of energy from the track battery 2TB to the rails of section 23T, and the connection of the track relays ZHTR and ZDTR across the rails of section 2-3T are governed by a code transmitter 2CT. The code transmitter ZCT is arranged and constructed so that when energy is supplied thereto over its operating circuit, the code transmitter will be operated in such manner as to close its front contact a for a predetermined time interval, of sufiicient duration to permit the impulses to be transmitted through each section to the opposite end of the single track stretch, and to thereafter close its back contact a for a relatively longer time interval to permit an impulse from the opposite end of the stretch to operate the track relays ZHTR or 2DTR. Additionally, the code transmitter ZCT is arranged and constructed so that its cycle of operation starts from an initial point each time the supply of energy is established thereto. Such a code transmitter may be of the well-known motor driven type, with suitable cams to determine the sequence of opening and closing the contacts, or 'it may comprise a combination of a conventional pendulum type of code transmitter wellknown in the art, together with a chain of relays which are picked up and released in accordance with the operation of the contacts of these pendulum coders. The actual form which the .code transmitter ZCT takes forms no part of my invention, and it may comprise an arrangement such as that shrown in Letters Patent of the United States No. 2,496,607, granted to me on February 7, 1950.

y The code transmitter ZCT is shown in the condition which it assumes when energy is being supplied from the track battery 2TB to the rails of section 2-3T. At this time, the positive terminal of battery 2TB is connected to the track rail 2 of section 2-3T by a circuit including front contact a of relay lDGP, and the frontcontact a of the code transmitter ZCT. The negative terminal of the battery is connected to the rail 1 of section 2-3T over front contact b of relay lDG-P.

Relay IDGP is a signal repeater relay, which is energized when and only when signal 18 indicates clear, and serves to pole-change the supply of energy to the track section 23T, in order to govern the indication on the distant signal 38 as will be subsequently described. The circuit for energizing the code transmitter ZCT is governed by a circuit including the back contacts a of track relays ZHTR and ZDTR, so that in the event that either of these track relays is picked up, the code transmitter ZCT cannot operate its contacts to disconnect the relay from the section rails.

The track relays ZHTR and ZDTR as well as the other code following track relays, are of the polar biased type, having contacts which are picked up when and only when current flows through the coil of the relay in the direction indicated by the arrow thereon. It will be seen that during the time that the contact a of the codetransmitter ZCT is released, the windings of relays ZHTR and 2DTR are connected in series across the rails 1 and 2 of track section 2-3T, so that energy supplied at the opposite end of section 2-3T at this time may flow through the windings of the relays, and cause one relay or the other to operate depending upon the polarity of the energy supplied over the track rails. As previously pointed out, the code transmitter ZCT is controlled over back contacts a of relays ZHTR and ZDTR in series, so that during the time that these relays are connected across the track rails, and are picked up by an impulse of energy, the code transmitter 2CT cannot interrupt the connection, since its contact a will remain released. The code following action of the track relays ZHTR and ZDTR is detected by the code detecting relays ZDTFP, 2HTFP and ZTBP. These relays are sufficiently slow in releasing their contacts to bridge the normal time in which the supply of energy to their windings is interrupted by the coding action of the track relay contacts b. However, if the contacts of the relays ZHTR and ZDTR remain in their picked up or released position for a time interval beyond the release time of the relays, the relays will thereupon release. Relay ZDTFP is a front contact repeater of relay ZDTR, and is energized and picked up when relay ZDTR is operating its contacts, relay ZHTFP is a front contact repeater of the relay ZHTR, and is picked up when relay ZDTR is released and relay ZHTR is picked up, while the relay 2TBP is a back contact repeater of both the 2HTR relay and the ZDTR relay. It will be obvious from the drawings that the relay ZTBP can only be picked up when one or the other of the front contact repeater relays ZHTFP or ZDTFP is picked up, and the contacts b of relays ZHTR and ZDTR are released. Accordingly, the relay ZTBP will be picked up when the code following track relays are operating upon either polarity of coded energy, and the relays ZHTFP and ZDTFP will be picked up in accordance with the particular track relay which is operating. As shown, the contacts of relays ZTBP and ZDTFP govern the supply of energy to the lamps of signal 25, in such manner that when relay ZTBP and relay ZDTFP are both picked up as a result of the operation of relay ZDTR, a circuit is established over front contact a of relay ZTBP and front contact b of relay ZDTFP to supply energy to the green lamp G of signal 28. When impulses of coded energy of the opposite polarity are supplied over the rails of section 2.3T, the relay ZI-ITR will operate its contacts in response to the code impulses, and accordingly, relays ZHTFP and ZTBP will be picked up, while relay ZDTFP will be released. At this time, a circuit will be established for lighting the yellow lamp of the signal 28, which circuit maybe traced from terminal B over front contact a of relay ZTBP, and over back contact b .of relay ZDT"? to the signal lamp ;Y and terminal N. When thesupply of 'coded energ'y from the track rails 2'-3T iscut off, both sweet of the code following track relays ZHTR, and ZDTR will release and remain released, so that after a shorttime interval, the contacts of the front contact repeater relays" 2HTFP or 2DTFP will be released, thus causing the release of back contact repeater ZTBP. When relay ZTBP is released, its back contact a establishes an obvious circuit for supplying energy to the red lamp R of signal 25. Accordingly, it will be seen that the aspect displayed by signal 25 will be governed by the presence or absence of coded energy in section 2-3T,.a yellow or caution aspect being displayed when the polarity of the code impulses is such as to operate the 'code following track relay ZHT R, a green or clear aspect being displayed when the polarity of the coded energy is such as to cause operation of relay ZDTR, and a red or stop aspect being displayed whenneither of the relays is operating.

Inspection of the drawings will show that the apparatus associated with signal 78 at the east end of the single track stretch, as shown in Fig. lb, is similar to that provided at the west end of the'stretch shown in Fig. 1a. The apparatus at the east end of the single track stretch functions in a manner similar to that described above for the apparatus at the west end of the stretch, that is, the code transmitter 7CT functions in such man ner as to cause impulses of energy of one polarity or the other depending upon the position of the contacts of the signal repeating relay SDGP to be supplied to the track section 6-7T during the time that the contact a of the code transmitter is picked up. During the time that contact a of the code transmitter 7CT is released, the track relays 7DTR and 7HTR are connected across the section rails, and respond to impulses supplied over the section rails from the distant signal location. As pointed out in connection with the apparatus at signal location 1S-2S at the west end of the single track stretch, the code transmitter 7CT is arranged and constructed so that the impulse which is supplied to the rails of section 6-7T is of a relatively long duration to allow the energy to be transmitted to the succeeding track sections to the west end of the stretch, and the duration of the interval in which the track relays 7DTR and 7HTR are connected to the rails is suificiently long to allow an impulse transmitted from the West end of the single track stretch to be supplied through the track section to pick up the relay 7DTR or 7HTR in accordance with the polarities of the code pulse. The leaving signal 78 governing train movements westward into the single track stretch is governed in a manner similar to that describedabove for the leaving signal 28 governing eastbound movement into the west end of the stretch, that is, when the impulses of energy supplied from the distant signal location over the rails 1 and 2 of section 6-7T are of such polarity as to cause operation of the contacts of relay 7DTR, signal 78 will display a green or clear aspect, and when the polariy of the impulses are such as to cause operation of the contacts of relay 7HTR, the signal 78 will display a yellow or caution indication, and when neither of the track relays is operating, due to a train shunting the rails, or an interruption in the supply of coded energy, the code detecting relays will be released and the signal 78 will display a red or stop aspect.

Having thus described the construction and operation of the apparatus located at the ends of the single track stretch, it is believed that the description of the apparatus located at the intermediate signals on the single track stretch will be facilitated by describing the operation of the equipment associated with the entire single track stretch under various conditions.

Under normal conditions, as shown in the drawings, with no train occupying the stretch, each time that the code transmitter'ZCT at the left-handend of the stretch closes its front contact a, a pulse of energy is supplied to the track rails 1 and 2 of section 2-3T and is supplied over the rails of the section to the track relays 3HTR and 3DTR located at the opposite end of the section. At this time, signal 18 is-displaying a clear aspect, relay iDGP will 'b'e picked up, and accordingly, energy is supplied from the positive terminal of batter 2TB over front contact a of relay lDGP, front contact a of the code transmitter ZCT, rail 2 of section 2-3T, through the windings of relays 3DTR and 3HTR in series, over front contact a of relay 4TPP, back contact b of relay 4TP, and over the rail 1 of section 2-3T and front contact b of relay lDGP to the negative terminal of battery 2TB. The flow of energy through the windings of the relays 3HTR and 3DTR at the east end" of section 2-3T is such that relay 3DTR will pick up its contacts, while relay 3HTR will remain released. H

Since the polarity of the impulses supplied over section 2-3T are such as to cause operation of relay 3DTR, relay 3DTFP will be energized each time that relay 3DTR picks up, by a circuit which may be traced from terminal B at back contact d of relay 4SR, front contactbof relay 3DTR, and the winding of 3DTFP to terminal N. Relay 4SR is a directional stick relay which has its contacts picked up only when a train moves by signal 48, and remains picked up while the train moves through the remainder of the single track stretch in advance of signal 48, as will be subsequently described in detail. During the time relay 3DTR is released, this circuit serves to supply energy to the winding of relay 3TBP over front contact a of relay SDTFP, which relay is sufiiciently slow in releasing to bridge the periods in which the relay 3DTR is released. Accordingly, relay 3TBP will be picked up at this time, in addition to relay 3DTFP which is the front contact repeater of relay 3DTR. As a result, thegreen lamp G of signal 35 Will be lighted by a circuit including front contact b of relay 3TBP and front contact b of relay 3DTFP.

When relay 3DTR picks up, its front contact a establishes a circuit for energizing the code transmitting relay 4HDTP associated With track section 4-5T. This circuit may be traced from terminal B at front contact a of relay STBP, through back contact a of relay 3AP, back contact c of relay 4TP, front contact a of relay 3DTR, and the winding of relay 4HDTP to terminal N. When contact a of relay 4HDTP picks up, it connects the battery 4TB across the rails of section 4-5T. Accordingly, energy flows from the positive terminal of battery 4TB over front contact a of relay 4HDTP, rail 2 of section 4-5T, back contact a of relay 6HDTP, the winding of relay 5TR from left to right, and rail 1 of section 45T to the negative terminal of battery 4TB. The direction of flow of energy through the winding of relay STR is such that relay 5TR will pick up its contacts in response to the supply of code impulses from the rails of section 4-5T. According'ly,code detecting relays 5TFP- and STBP will be picked up at this time. With contact 0 of relay STBP picked up, an obvious circuit is established for supplying energy to the green lamp G of signal 58.

The code transmitting relay 5TP is supplied with energy at this time by a circuit which may be traced from terminal B over back contact b of relay 6HDTP, front contact a of relay STBP, front contact b of relay STR, and the winding of relay STP to terminal N. When relay STP picks up, its front contact a interrupts the circuit for supplying energy to the winding of relay STPP, so that relay STPP will be released. With relay 5TP picked up, a circuit is established for supplying energy to the rails of section 6-7T, and through the winding of relay 7DTR at the other end of the section. This circuit may be traced from the positive terminal of battery 6TB, through the winding of approachrelay 6AR, back contact b of the directional stick relay SSR, rail 1 of section 6-7T, back contact a of the code transmitter 7CT, the windings of relays 7DTR and 7HTR in series, over rail 2 of section 6-7T, front contact 12 of relay 5TP, and back contact a of relay 58R to the negative terminal of battery Accordingly, relay 7DTR is supplied with energy:

of the proper polarity to cause this relay to pick up its contacts.

It will be seen, therefore, that when the single track is vacant and energy is supplied to the west end of the stretch by picking up of contact a of the code transrnitter 2CT, the impulse is repeated through the successive track sections to the right-hand or east end of the stretch to pick up the track relay- 7DTR at this point.

After a short interval thesupply of energy to the west end of the stretch is cut ofi by contact a of relay ZCT opening, so that energy is no longer supplied to the winding of relay 3DTR, and relay 3DTR releases. When contact a of relay 3DTR releases, it interrupts the circuit for energiiing relay 4HDTP, and when relay 4HDTP releases it interrupts the supply of energy from battery 4TB to the rails of section 4-5T. Accordingly, relay STR at the east end of section 4-5T will be released and its contact b will interrupt the circuit for supplying energy 'to the code transmitting relay STP. When relay STP releases, its contact b interrupts the supply of energy to the rails of section 67T, with the result that relay 7DTR at the east end of the stretch is deenergized and its contacts release.

With the contacts of relays 7DTR and 7HTR released, a circuit is established over back contacts a of these relays to supply energy to the code generating means 7CT, which operates to pick up its contact a, thereby connecting the battery 7TB across the rails of section 6-7T at the east end thereof. Energy is now supplied to the winding of relays 6DTR and 6HTR at the west end of the section 6-7T by a circuit which may be traced from the positive terminal of battery 7TB, over front contact a of relay SDGP, which relay is picked up at this time with signal 88 indicating clear, front contact a of code generator 7CT, rail 1 of section 6-7T, the windings of relays 6DTR and GHTR, front contact a of relay STPP, which is energized when relay STP is released, back contact b of relay STP, rail 2 of section 67T, and front contact -b of relay 8DGP to the negative terminal of battery 7TB. The direction of flow of energy through the winding of relay GDTR is such that relay 6DTR will pick up its contacts. When contact b of relay 6DTR picks up, it establishes a circuit for supplying energy to the Winding of relay 6DTFP, which circuit includes a back contact d of the directional stick relay SSR. The sup ply of energy to relay 6TBP is governed by a circuit including back contact d of relay 53R, back contact b of relay-s 6DTR and SHTR, and front contact a of relay 6DTFP. As previously explained, the relays 6DTFP,

6HTFP, and 6TB? are arranged and constructed so that their contacts are slow enough in releasing to bridge the intervals during which the supply of energy to their windings is interrupted by the normal coding action of the relays GDTR and SHTR. Accordingly, at this time relay GDTFP and the relay GTBP will be picked up, so

that a circuit including front contacts b of relays 6TBP and 6DTFP is established for supplying energy to the green lamp G of signal 65. Additionally, at this time the code transmitting relay 6HDTP is energized by a circuit which may be traced fro-m terminal B at front contact a of relay eTBP, over back contact a of relay 6A1, backcontact c of relay STP, front contact a of'relayoDTR, and through the winding of relay GHDTP to terminal N. When relay cI-IDTP picks up, its front contact :1 establishes a circuit for connecting the battery 5TB across the rails of section 4-5T at the east end thereof. Accordingly, energy is supplied to the track relay 4TR at the west end of the stretch by a circuit which may be traced from the positive terminal of battery 5TB, over front contact a of relay oHDTP, rail 2 of section 4 5T, back contact a of relay 4HDTP, the winding of relay 4TR from right to left, and rail 1 of sect-ion 4-5T to the negative terminal of battery 52.13. The direction of'fiow of energy through the winding of relay 4TR is such'that relay 4TR will pick upits contacts. As are sult of the operation of contact a of relay 4TR, relays 4T FP and 4TBP will be picked up and contact c of relay 4TBP establishes an obvious circuit for supplying energy to the green lamp G 'of signal 45. Additionally, when relay 4TR picks up a circuit is established for supplying energy to the winding of code transmitting relay 4TP, which circuit maybe traced from terminal B at back contact b of relay 4HDTP, front contact a of relay 4TBP,

. front contact b of relay 4TR, and the winding of relay 4T? to terminal N. When relay 4TP picks up, its front contact b establishes a circuit for supplying energy from the track battery 3TB to the rails of section 23T at the east end thereof. This circuit may be traced from the positive terminal of battery 3TB through the winding of the approach relay 3AR, over back contact b of directional stick relay 48R, rail 2 of section 23T, back contact a of the code generator ZCT, the winding of relays 2I-ITR and ZDTR in series, section rail 1 of section 23T,.front contact b of the relay 4TP, and back contact a of relay 48R to the negative terminal of bat tery 3TB. The direction of flow of energy through the winding of relay ZDTR is such as to cause relay 2DTR to pick up its contacts. As previously explained, the operation of relay ZDTR causes the relays 2DTFP and ZTBP to be picked up, so that a circuit is established for supplying energy to the green lamp G of signal 28, this circuit including front contact a of relay 2TB? and front contact b of relay ZDTFP.

After a short time interval, the contact a of the code transmitter 7CT at the east end of the single track stretch opens, thereby interrupting the supply of energy to the rails of section 6-7T of the east end of the stretch, thus deenergizing relay 6DTR. When relay 6DTR releases, its front contact a interrupts the circuit for relay 6HDTP, which upon releasing, interrupts the circuit for connecting battery 5TB across the rails of section 45T. Accordingly, relay 4TR at the west end of section 45T will release, and its front contact b will interrupt the circuit for the code transmitting relay 4TP which governs the connection of the battery 3TB to the rails of section 2-3T. With the supply of energy to section 2-3T cut off, the relay 2DTR at the west end of section 23T will release its contacts.

As long as the single track stretch is vacant the operation described above is continuously repeated, that is, an impulse of energy is supplied to the left hand or west end of the stretch and is repeated throughout the stretch to the right hand or east end where it picks up the track relay'7DTR so that signals 73, 5S and 38 display a clear aspect. When the impulse of energy at the west end of the stretch is cut oif, the track relays throughout the stretch release in sequence, and when the relays at the east end of the stretch release, the cod generating means is activated to supply an impulse of energy at the east end of the stretch which is repeated throughout the track sections in the stretch to the west end of the stretch, so that the signals 28, 4S and 68 display a clear aspect.

With the apparatus operating in its normal condition as described above, it will now be assumed that an east bound train approaches the west end of the single track stretch. When such a train approaches within a predetermined distance of the west end of the stretch, signal 15, which is governed in the conventional manner by circuits controlled by traffic conditions in advance, will be put to stop, and accordingly, relay lDGP will be released. When contacts a and b of relay lDGP release, the polarity of the impulses of the code energy supplied to the rails of section 2-3T is reversed. As a result, the flow of energy through the windings of relays SHTR and 3DTR in series at the east end of the stretch is reversed, so that relay 3DTR no longer operates its contacts and relay SHTR operates its contacts. The operation of the contact b of relay 3HTR causes the relay 3HTFP to be energiz'ed "and its contact a in the circuit for governing the supply of energy'to the back contact repeater STBP is closed. As a result of the cessation of the operation of the contact b of relay 3DTR, relay SDTFP will release its contacts after a short time interval, but as previously explained contact a of relay 3HTFP is now energized so that the supply of energy to the winding of relay 3TBP is continued. Accordingly, at this time a circuit is established for supplying energy to the yellow lamp Y of signal 38 over front contact b of relay STBP, and back contact b of relay SDTFP. In the circuit for governing the code transmitting relay 4HDTP, it will be seen that front contact a of relay 3HTR is in multiple with the front contact a of relay 3DTR, so that even though the contact a of relay 3DTR is no longer operating, relay 4HDTP will continue to operate each time that the front contact a of relay 3HTR picks up. Accordingly, the supply of impulses of energy to the section 4-5T are continued at this time, causing operation of relay STR at the east end of section 4-5T, which in turn causes signal 55 to continue displaying its clear aspect, and the operation of contact b of relay STR causes the continued operation of the code transmitting relay STP, so that impulses of energy continue to be supplied to the west end of section 6-7T thereby operating relay 7DTR at the east end of the section so that signal 78 continues to display its clear aspect. From the foregoing, it willtbe seen that while the train is approaching signal 28 at the west end of the stretch, signal 18 will be conditioned to display a stop or red aspect, while signal 38 will display a yellow or caution aspect, and signals 68 and 73 will display their clear, aspect. When the train passes signal 25, the wheels and axles of the train shunt the track circuit 23T, so that energy is no longer supplied to the windings of relays 3HTR and 3DTR at the east end of this section. When contact b of relay 3HTR ceases operation, it interruptsthe supply of energy to the winding of relay 3HTFP and after a short time interval contact a of relay 3HTFP interrupts the circuit for governing relay 3TBP which thereafter releases. When contact b of relay 3TBP releases it interrupts the circuit for supplying energy to the yellow lamp Y of signal 38 and establishes an obvious circuit for supplying energy to the red lamp R of the signal. Additionally, with contacts a of relay 3HTR and 3DTR both open, the code transmitting relay 4HDTP is no longer operated, so that the supply of energy to section 4-5T from battery 4TB is discontinued. This results in the cessation of operation of the contacts of relay 5TR, and the release in sequence of the code detecting relays STFP and 5TBP. When contact c of relaySTBP releases, the supply of energy to the green lamp G of signal 58 is interrupted and energy is supplied to the red lamp R of the signal, so that signal 58 indicates stop at this time. When contact b of relay STR releases and remains released, the supply of energy to the winding of relay 5TP is interrupted, and its contact b releases and remains released to thereby interrupt the supply of impulses of coded' energy to the west end of section 67T. Accordingly, relay 7DTR at the east end of section 6-7T will cease operation, and as a result relay 7DTFP and relay 7TBP will release in sequence, so that the supply of energy to the green lamp G of signal 78 is interrupted and the red lamp R of signal 75 is lighted to indicate stop. With relays 7DTR and 7HTR remaining in their released position, the circuit for supplying energy to the code transmitter 7CT is maintained continuously, so that the code transmitter 7CT continues to operate to periodically supply an impulse of energy to the east end of section 6-7T. These impulses of energy cause operation of relay 6DTR at the west end of section 6-7T, since the relay 8DGP is picked up at this time due to signal 85 indicating clear. Since relay 6DTR continues to operate, the circuit previously described for governing the operation of relay 6HDTP continues to be established in response to the supply of impulses of energy to the winding of relay 6DTR, so that these impulses are repeated into section 4-5T as a result of operation of relay These impulses of energy supplied to section 4-5T cause opera-,

tion of relay 4TR, which in turn causes the signal 48 tocontinue to display its clear aspect and in addition the contact b of relay 4TR continues to cause the operation of the code transmitter 4TP so that energy is being supplied at this time to the rails of section 2-3T from the battery 3TB, while the advancing east bound train occupies section 2-.3T.

When the east bound train advances within a predetermined distance of signals 38 and 48, the value of current which flows through the winding of approach relay 3AR will increase to the point that relay 3AR will commence to operate, and its contact a will recurrently supply energy to the slow release repeating relay 3AP. When relay 3A? picks up, its back contact a additionally interrupts the circuit for supplying energy to the code transmitting relay 4HDTP, which circuit is already opened by the release of the contacts a of relays 3HTR and 3DTR, and when contact b of relay SAP picks up it establishes a pick-up circuit for energizing the directional stick relay 45R. This pick-up circuit may be traced from terminal B through back contact a of relay STBP, front contact b of relay 3AP, front contao't b of relay 4TBP and the winding of relay 4SR to terminal N, so that relay 4SR picks up at this time. When the east bound train passes signal 48, relay 4TR will cease its code following operation due to the shunting of section 4-5T by the wheels and axles of the train, so that contacts a and b of relay 4TR will release and remain released. This will cause relay 4TBP to release, and when this relay releases, its contact c interrupts the supply of energy to the green lamp G of signal 43 and establishes the supply of energy to the red lamp Rof the signal, so that signal 48 displays a red aspect. Additionally, when relay 4TBP releases, a stick circuit for relay 48R is established which may be traced from terminal B at front contact d of relay 45R, through back contact b of relay 4TBP, and through the winding of relay 48R to terminal N. When front contact d of relay 4SR picks up, it also establishes the supply of energy to the operating winding of a conventional code transmitter CT, which is constructed and arranged so that its contact a operates to open and close 75 times per minute.

A circuit is now established for governing the operation of the code transmitting relay 4TP independently of the code following operation of relay 4TR, which circuit may be traced from terminal B at back contact b of relay.4HDTP, through back contact a of relay 4TBP, front contact c of relay 4SR, front contact a of the code transmitter 75CT, and the winding of relay 4TP to terminal N. Accordingly, the contacts of relay 4TP will pick up and release at the rate of 75 times per minute, even though relay 4TR is continuously released at this time.

At this time also, since contacts a and b of relay 48R are picked up, the polarity of the energy supplied from the battery 3TB to the rails of section 2-3T is reversed to provide impulses having a polarity opposite to those previously described. These impulses are not transmitted to the west end of the section at this time, since the rear end of the train is still occupying the section 2-3T.

When the east bound train vacates section 2-3T, since the directional stick relay 45R is now picked up, energy will again be supplied from the battery 3TB to the section 2-3T as a result of the operation of relay 4TP governed by the code transmitter 75CT. This fiow of energy may be traced from the positive terminal of battery 3TB through the winding of relay 3AR, front contact a of relay 4SR, front contact b of relay 4TP, section rail 1 of section 2-3T, the windings of relays ZHTR and ZDTR, back contact a of the code generating device ZCT, rail 2 of section 2-3T, and front contact b of relay 48R to the negative terminal of battery 3TB. Accordingly, the flow of energy to the winding of relays ZHTR and ZDTR is such: as to cause the contactsof relay ZHTR to operate,

11 with the result that relay ZHTFP. and relay ZTBP will be energized and their contacts picked up. Since, relay ZTBP is picked up and relay ZDTFP is released at this time, energy will be supplied to the yellow lamp Y of signal 28 over front contact a of relay ZTBP and back contact b of relay ZDTFP, so that signal 28 will display a yellow or caution aspect thereby permitting a following train to enter the single track section while the portion of the stretch in advance of the intermediate signal is occupied by a preceding train.

During the time that section 2-3T is occupied by the east bound train, the relays ZHTR and 2DTR are continuously released so that the supply of energy to the code transmitter 2CT is continuously established with the result that contact a of code transmitter 2CT is recurrently picked up to supply coded energy from battery 2TB to the rails of section 23T. Accordingly, when the train vacates section 23T, this energy causes the operation of relay 3DTR, since the pole changing relay lDGP is now picked up. Although contact b of relay 3DTR is operated at this time, the relays SDTF P and STBP will remain released, since the supply of energy thereto is interrupted at back contact d of relay 48R, which relay is picked up while the train occupies the portion of the stretch in advance of signal 43. It follows that signal 38 will continue to display a red aspect in the rear of the east bound train. When the rear end of the train vacates section 2-3T, the supply of energy from battery 3TB is reestablished, but the flow of current through relay 3AR is insuflicient to cause operation of the contacts of this relay, so that relay 3AP releases and remains released. The release of contact b of relay 3AP interrupts the previously described pick-up circuit for relay 45R, but relay SSR remains stuck up since its stick circuit is still closed at back contact b of relay 4TBP.

From the foregoing, it will be sen that a train entering the single track stretch from the west end thereof will cause signal 28 to display a red aspect during the time the train occupies end section 23T, but when the train passes the intermediate signal 48 and the rear end vacates the end section, the directional stick relay 45R will be picked up to thereby cause operation of the code transmitting relay 4TP as a result of energization of the code transmitter 75CT, and in addition, the polarity of the impulses supplied from the east end of section 2-31 will be reversed so that the leaving signalZS at the west end of the stretch will display a yellow or caution aspect, thereby permitting a following train to move into this section. When the east bound train moves by signal 68 and enters section 641, the supply of energy to the winding of relay 6DTR is interrupted, so that relay 6DTR releases its contacts and they remain released while the train occupies the section. The cessation of operation of the contact b of relay 6DTR results in the release of relays '6DTFP, and 6TBP so that the supply of energy to the green lamp G of signal 65 is interrupted and back contact b of relay 6TBP establishes a circuit for supplying energy to the red lamp R of signal 68; Moreover, the contact a of relay 6DTR cuts oil the supply of energy to the code transmitting relay eHDTP, so that the contact a of relay 6HDTP releases and remains released, thereby cutting off the supply of energy from relay TB to the rails of section 45T, and continuously connecting the winding of relay STR across the section rails. Since relay STBP remains released at this time because the directional stick relay 4SR is still energized, front contact a of relay STEP interrupts the circuit for the supply of energy to the code transmitterrelay 4HDT P so that when the rear end of the section vacates section 4-5T no energy is supplied to the section. Relay STR therefore remains released with the result that relay STBP also remains released and its contact 0 continues to inter-- rupt the circuit for the green lamp G of signal 58 and supply energy to the red lamp R of the signal.

When the east bound train in section 6-7T moves by I signal 88, at the east end of the stretch, signal 85 will go to stop, and relay SDGP will accordingly be released. Since the relays 7DTR and 7HTR are continuously released at this time, the code transmitter 7CT will continue to operate, so that its contact a recurrently connects the battery 7TB across the section rails, and since relay SDGP is released at this time, the impulses of coded energy supplied at the east end of section 6-7T are reversed in polarity from those normally supplied to the section rails.

When the rear end of the train vacates section 6-7T, so that the entire single track stretch is vacated, the impulses of energy from battery 7TB which are supplied to the rails of section 6-7T flow to the west end of the section and since relay STP is now released and relay STPP is picked up, are supplied to the windings of relays 6DTR and 6HTR in series. At this time the direction of flow of energy through the winding of relay 6HTR is such as to cause the relay contacts to operate. The operation of front contact b of relay 6HTR causes energy to be supplied to the winding of relay 6HTFP, which picks up its front contact a so that energy is supplied to the winding of relay 6TBP each time that contact b of relay 6HTR releases. Accordingly, relay 6TBP will be picked up at this time and relay 6DTFP will be released since relay 6DTR will not operate its contact. With contact b of relay 6TBP picked up, a circuit is established for supplying energy to the yellow lamp Y of the distant signal 68 which circuit includes back contact b of relay 6DTFP. Additionally, energy is now supplied to the winding of relay 6HDTP by a circuit which may be traced from terminal B at front contact a of relay 6TBP, through back contact a of relay 6AP, back contact 0 of relay STP, front contact a of relay GHTR and the winding of relay 6HDTP to terminal N. Accordingly, each time that relay 6HTR picks up, energy is supplied to the winding of relay eHDTP and its front contact a picks up to connect the track battery 5TB across the rails 1 and 2 at the east end of section 4-5T. The supply of impulses of energy to section 4-5T at the east end thereof causes the code following operation of the track relay 4TR at the west end, so that the code detecting relays 4TP? and 4TBP become picked up, and contact 0 of relay 4TBP establishes the supply of energy to the green lamp of signal 48 and cuts off the supply of energy to the red lamp R of the signal.

Additionally, when contact b of relay '4TBP picks up, the stick circuit for relay 4SR is interrupted and the relay 45R releases. With the stick relay 48R released, and the relay 4TBP picked up, the circuit for supplying energy to the code transmitting relay 4TP over the contact a of the code transmitter CT is interrupted at back contact a of relay 4TBP and front contact 0 of relay 48R and the relay 4TP is now operated by energy supplied over the circuit including back contact b of relay 4HDTP, front contact a of relay 4TBP, and front contact b of the track relay 4TR, so that the operation of the code transmitting relay 4TP is again made dependent on the code following operation of relay 4TR.

Since relay 48R is now released, its contacts a and b reverse the polarity of the energy supplied from battery 3TB, so that each time the contact b of relay 4TP picks up and connects the battery 3TB to the rails of section 2-3T relay ZDTR at the west end of the section picks up. The resultant recurrent operation of the contacts of relay 2DTR causes the relays ZDTFP and relay ZTBP to be picked up, so that energy is now supplied to the green lamp G of signal 25, and the supply of energy to the yellow lamp Y of the signal is cut off. Each time an impulse of energy from the east end of section 2-31" is interrupted, relay ZDTR releases its contacts so that energy is supplied over the back contacts a of relays ZHTR and ZDTR to the code transmitter ZCT, which thereupon picks up its contact a momentarily to supply an impulse of energy to the rails of section Z-ST-at the stagger west end thereof. These impulses of energy pick up the contacts of relay 3DTR at the east end of the section, so that contact b of relay 3DTR in the circuit for supplying energy to the relay 3DTFP operates with the result that relays 3DTFP and 3TB? pick up and establish a circuit for supplying energy to the green lamp G of signal 38 and cut off the supply of energy to the red lamp R of the signal. Also, the operation of contact a of relay 3DTR causes energy to be recurrently supplied to-the winding of relay 4I-IDTP, so that the impulses are repeated into the west end of section 4-5T. These latter impulses cause operation of relay STR at the eastend of the section, and result in the picking up of the code detecting relays STFP and STBP, so that the green lamp G of signal 53 isnow lighted and the red lamp R extinguished. t

Relay STP, governing the supply of energy to the west end of section 6-7T is nowoperated as a result of the operation of contact b of relay STR, so that impulses of energy are supplied at the west end of section 6-7T. These impulses have a polarity which causes operation of relay 7DTR at the east end of the section, and the operation of this relay, in turn results in signal 73 again displaying a green aspect.

When the east bound train advances sufiiciently far in advance of signal 88, the signal will again display its clear aspect, and accordingly relay 8DGP will pick up its contacts. Consequently, the polarity of the coded energy supplied to the rails ofsection 67T from battery 7TB will be restored'to its normal condition. of the energy will now be such that relay 6DTR at the west end of section,6,-7T will operate and relay 6HTR will cease operating. "The code-following operation of contact b of relay 6DTR causes relays GDTFP and 6TBP to be picked up, so that the yellow lamp of signal 68 is extinguishedand energy is supplied to the green lamp G of the signal. Accordingly, the apparatus is now restored to its normal condition as previously described.

It will be seen that the arrangement of equipment is symmetrical for the two directions of traffic, so that the equipment operates in a similar manner for the movement of a west bound train through the single track stretch, and as a result, a detailed description of the operation of the equipment for a west bound train movement is deemed unnecessary.

From the foregoing, it will be apparent that my invention provides, in a coded track circuit railway signaling system of the type described in the above-referred-to Young application, an arrangement for permitting following moves moves to be made into single track stretches equipped with apparatus of the Young type, by providing an intermediate signal location for each direction of movement, such signals being most generally located opposite the distant signal provided for the station'entering signals. This arrangement includes a suitable directional stick relay, arranged to be picked up in advance upon movement of a train in a specified direction, which directional stick relay serves to connect an auxiliary code generating device across the rails of the section to supply coded impulses to the section in the rear of a train. Also, the directional stick relay serves to reverse the polarity of the coded energy impulses, so that when the intermediate signal is at stop the polarity of impulses supplied to the section between the intermediate signal and the station leaving signal is such as to cause the station leaving signal to display a caution aspect, thereby permitting a second train to advance into the single track stretch.

Although I have herein shown and described only one form of polartcoded track circuit railway signaling system embodying my invention, it is to be understood that various changes and modifications therein may be made within the scope of the appended claims without departing from the spiritand scope of my invention.

The polarity Having thus described my invention, what I'claim is.

1. In combination, a stretch of single track railway ex-' tending between a first and a second location, the rails of said stretch being divided into a plurality of track sections including a first end section at one end of said stretch and a second end section at the other end of said stretch, each of said track sections having at each end thereof code following track relay means operated by energy supplied over the section rails from the other end of the section, code impulse generating means at the ends of said end sections adjacent said first and second locations effective to supply impulses of energy to the railsof the associated end section of said stretch, code transmitting means for each end of each track section in the stretch except the ends of said end sections adjacent said first and second locations for supplying to the section rails impulses of coded energy of a first polarity dependent on code following operation of the track relay means at the adjacent end of the adjoining track section, whereby when the stretch is vacant the application of coded energy to an end of the stretch results in the supply of coded energy to the corresponding end ofeachtrack section in the stretch, a signal at each end of the stretch governing entrance of traflic into the stretch, control means for each signal governed by the associated track relay means, means for said end sections. away from said first and second locations controlled by the approach of trains leaving said first and'second locations for reversing the polarity of said code transmitting means, and means for operating said .code transmitting means independently of the code following operation of the track relay means for the adjacent end of theadjoining section for supplying coded energy of said reversed polarity to the rails of said end sections when a train is occupying said stretch and moving away from the end section.

1 2. In combination, a stretch of single track railway extending between a first and a second location, the rails of said stretch being divided into a plurality of track sections including a first end section extending between said first location and a first intermediate point, and a second end section extending between said second location and a second intermediate point,each of said track sections having at each end thereof code following track relay means operated by coded energy supplied over the section rails from the other end of the section, code impulse generating means at said first and second locations effective to supply impulses of energy to the rails of the associated end sections of said stretch at the ends of said end sections adjacent said first and second locations, code transmitting means for each end of each track section in the stretch except the ends of said end sections adjacent said first and second locations for supplying to the section rails impulses of coded energy of a first polarity dependent on code following operation of the track relay means at the adjacent end of the adjoining track section, whereby when the stretch is vacant the application of coded energy to one end of the stretch results in the supply of coded energy to the corresponding end of each of the track sections in the stretch, a signal at each end of the stretch governing entrance of traffic into the stretch, control means for each signal governed by the associated track relay means in a manner dependent on the polarity of the coded energy received, means responsive to approach to said intermediate points for reversing the polarity of said code transmitting means, and means located at said intermediate points for operating said code transmitting means independently of the code following operation of the track relay means for the adjacent end of the adjoining section when a train is occupying said stretch and moving away from said intermediate point.

3. In combination, a stretch of single track railway extending between a first'and a second location, the rails of said stretch being divided into a plurality of track sections including a first end section atone end of said stretch and a second end section at the other end of said stretch, each track section in said single track stretch having at each end code following track relay means, code generating means at each end of said single track stretch effective when rendered active to supply impulses of energy to the rails of the associated end section at the ends of said end sections adjacent said first and second locations, each of said code generating means being governed by the associated track relay means and when rendered active operating to supply an energy impulse to the rails of the associated section following each deenergization of the track relay means and thereafter operating as long as the track relay means remains deenergized to supply said impulses at predetermined intervals, each track relay means for the sections in said stretch except the track relay means at the ends of said end sections adjacent said first and second locations having associated therewith means responsive to code following operation of said track relay means for supplying coded energy to the adjacent end of the adjoining track sections, whereby when the single track stretch is vacant the application of coded energy to an end of the single track stretch results in the supply of coded energy to the corresponding end of each track section in the single track. stretch, a leaving signal at each end of the stretch gov-- erning the movement of traffic into said stretch, control means for each of said leaving signals governed by the track relay means at the adjacent end of the associated end section and selectively responsive to the polarity of the energy supplied over the rails of said end section, a first intermediate signal governing the movement of traffic from said first end section into the portion of the single track stretch in advance of said first intermediate signal, a second intermediate signal governing the movement of traffic from said second end section into the portion of the single track stretch in advance of said second intermediate signal, directional control means associated with each of said intermediate signals and rendered effective when a train occupies the portion of the single track stretch in advance of the intermediate signal and is near said intermediate signal, code generating means governed by said directional control means and effective when a train is receding from said intermediate signal to supply coded energy to the adjacent end of the associated end section independently of the code following operation of the track relay means for the adjoining section, and pole changing means governed by said directional control means for changing the polarity of the coded energy supplied to said end section at the end thereof adjacent said intermediate signal.

4. In combination, a stretch of single track railway extending between a first and a second location, the rails of said stretch being divided into a plurality of track sections including a first end section at one end of said stretch and a second end section at thesother end of said stretch, each track section in said single track stretch having at each end a code following track relay means, code generating means at each end of said single track stretch effective when rendered active to supply impulses of energy to the rails of the associated end section at the ends of said end sections adjacent said first and second locations, each of said code generating means being governed by the associated track relay means and when rendered active operating to supply an energy impulse to the rails of the associated section following each deenergization of the track relay means and thereafter operating as long as the track relay means remains deenergized to supply said impulses at predetermined intervals, each track relay means for the sections in said stretch except the track relay means at the extreme ends of said end sections adjacent said first and second locations having associated therewith means responsive to code following operation of said track relay means for supplying coded energy to the adjacent end of the adjoining track sections, whereby when the single track stretch is vacant the application of coded energy to an end of the single track stretch results in the supply of coded energy to the corresponding end of each track section in the single track stretch, a leaving signal at each end of the stretch governing the movement of traffic into said stretch, control means for each of said leaving signals governed by the track relay means at the adjacent end of the associated end section and selectively responsive to the polarity of the energy supplied over the rails of'said end section, a first intermediate signal governing the movement of traffic from said first end section into the portion of the single track stretch in advance or" said first intermediate signal, a second intermediate signal governing the movement of traffic from said second end section into the portion of the single track stretch in advance of said second intermediate signal, directional control means associated with each of said intermediate signals and rendered effective when a train occupies the portion of the single track stretch in advance of the intermediate signal and is receding from said leaving signal, code generating means governed by said directional control means and effective when rendered active to supply coded energy to the adjacent end of the associated end section independently of the code following operation of the track relay means for the adjoining section, and pole changing means governed by said directional control means for changing the polarity of the coded energy supplied to said end section at the end thereof adjacent said intermediate signal, said directional control means comprising a directional stick relay, an approach relay having contacts which are picked up when a train approaches said intermediate signal, a pick-up circuit for said directional stick relay including a contact of said approach relay, and a stick circuit for said stick relay governed by the track relay means for the adjoining end of the track section in advance of the intermediate signal.

5. in a coded track circuit signaling system for a stretch of single track in advance of a siding, a three aspect leaving signal for said siding, insulated joints located in said stretch for dividing said stretch into first and second sections, first track relay means adapted to be connected across said first section adjacent said joints, first repeater relay means energized by periodic actuation of said track relay means, an approach relay, a source of voltage and a pair of terminals connected in series with said approach relay, second track relay means connected across said second section adjacent said joints, second repeater relay means having a first pickup circuit controlled by said second track relay means, said second repeater relay means having front contact means for connecting said terminals across said first section for applying coded energy thereto, back contact means for said second repeater relay means for connecting said first track relay means across said first section, third repeater relay means controlled by said second track relay means, stick relay means for reversing said terminals, a pickup circuit for said stick relay including means operated by front contacts of said approach relay, a front contact of said third repeater relay means, and a back contact of said first repeater relay means, a stick circuit for said stick relay inciuding a back contact of said third repeater relay means, a code transmitting relay controlled by said stick relay, a second pickup circuit for said second repeater relay means controlled by said code transmitter, and means adapted to be connected across said first section adjacent said siding for controlling the aspect of said leaving signal in accordance with the polarity of said energy.

6. A coded track circuit signalling system for a stretch of single track in advance of a siding, comprising, in combination, a leaving signal for said siding having clear, caution and stop aspects, means dividing said stretch into a first section adjacent said siding and a second section, first track relay means for said first section, an approach relay for said first section having contacts which are picked up in response to a train in said first section approaching said dividing means, second track relay means for said second section, first repeater relay means controlled by a code following operation of said second track relay means, second repeater means having a first pickup circuit controlled by said second track relay means and said first repeater means, means adjacent said dividing means and controlled by said second repeater means for applying coded energy of a first polarity to said first section in response to code following operation of said second track relay means, stick relay means having a pickup circuit controlled by front contacts of said approach relay and said first repeater means and back contacts of said first track relay means for reversing the polarity of said code applying means, a stick circuit for said stick relay means including a back contact of said first repeater means, a code generator controlled by said stick relay means, a second pickup circuit for said second repeater means controlled by said code generator, and means responsive to coded energy in said first section for controlling said leaving signal to display its clear aspect on receipt of energy of said first polarity and its caution aspect on receipt of energy of reverse polarity.

7. In combination, a stretch of single track railway extending in advance of a given location, said stretch being divided into a first section, having a first end adjacent said given location and a second end, and a second section, having a first end adjacent the second end of said first section, first code following track relay means at the first end of said first section, a leaving signal at said given location operated by said code following means to display a first aspect in response to coded energy of a first polarity and to display a second aspect in response to coded energy of a second polarity supplied over the section rails from said second end thereof, second code following track relay means at the first end of said second section adapted to be operated by energy supplied over the second section rails, code transmitting means for said second end for supplying to the first section rails impulses of coded energy of a first polarity dependent on code following operation of said second track relay means, means at said second end of said first section responsive to approach of a train from said given location for reversing the polarity of said code transmitting means, and means for operating said code transmitting means independently of the code following operation of the track relay means for the second section for supplying coded energy of reversed polarity to the rails of said first section when a train is occupying said second section and moving away from said second end.

References Cited in the file of this patent UNITED STATES PATENTS 2,350,657 Wynn June 6, 1944 2,351,540 Pelican June 13, 1944 2,364,840 Zane et al. Dec. 12, 1944 2,401,20l Thompson May 28, 1946 2,408,206 Fereday Sept. 24, 1946 2,546,33l Butridge Mar. 27, 1951 2,558,473 Young June 26, 1951 2,662,971 Howard Dec. 15, 1953 2,703,839 Judge Mar. 8, 1955 

